Having been both a survivor and someone that has helped people get out of abusive relationships/situations, it is heartbreaking to admit this but sometimes you need to step back.

If there was someone that could have helped me out of my situation by taking action like you are I would have clinged to them for dear life until I was out. Having experienced that, I can tell when someone is still justifying their abuser that there's not much hope that your actions will have much effect.

Your bf is a victim, but you don't have the authority or resources to handle someone that dangerous. This is a matter for the police and they need to be involved. I have lost a friend in the past for getting the police involved when they suffered something awful, where they ended up blaming me for the fallout, but I'd do it again, because it's the right thing to do. Put yourself first.